1. Technical Field
The present disclosure relates to a serial data receiver of a data communication system, and more particularly to a circuit and a method of measuring eye size of serial data in a serial data receiver of a data communication system.
2. Discussion of the Related Art
A serializer-deserializer in a data communication system serializes data so as to transfer the serialized data via transmission lines, such as a printed line, and deserializes serialized data that is received.
Typically, the serializer-deserializer includes a preamplifier, an equalizer, a sampler, and a clock data recovery (CDR) circuit.
The serializer-deserializer recovers a frequency of the serialized data in the CDR circuit and supplies a clock signal with the recovered frequency to the sampler. Therefore, the receiver can receive the serialized data even though a transmitter operates and transmits the serialized data with a clock signal having a different frequency from that of a reference clock used in the receiver.
When data are transmitted at a high speed via a transmission line, such as a printed line, inter-symbol interference (ISI) may occur due to the properties of the transmission line. The amplitude and phase of the received data signal can be seriously distorted by the inter-symbol interference, and the distorted amplitude and phase may cause bit errors in the receiver. Thus, as the length of the transmission line becomes longer and the data transmission rate becomes higher, the distortion of the received signal increases.
Since the serializer-deserializer is a kind of a serial interface, the received serial data may include a high degree of jitter. Therefore, when flip-flops or latches used in the sampler receive the data, the eye size of the data is critical to the performance of the device or the entire system.
The preamplifier in the serializer-deserializer amplifies a voltage level of the received data and the equalizer in the serializer-deserializer executes an equalization of the received data to reduce jitter, specifically ISI, in the received data, and then outputs the equalized signal to the sampler.
The equalizer is provided with a control bit to adjust an equalizing strength, based on the jitter properties of the received data. The equalizer can control the equalization function based on the jitter properties. A relatively small eye size of the received data indicates that the equalization is inadequate, and then the equalizer strengthens the equalization. On the contrary, a relatively large eye size of the received data indicates that the equalization is excessive, and the equalizer weakens the equalization so as to obtain an optimized eye size.
The conventional serializer-deserializer uses a decision feedback circuit to detect a variation of the eye size of the signal, instead of directly measuring the eye size of signal at an output node of the equalizer.